Chronic Effects of [D-Trp6-Pro9-NEt]Luteinizing Hormone-Releasing Factor on Reproductive Processes in the Female Rat*

Abstract

LRF and one of its highly potent analogs, [D-Trp⁶-Pro⁹-NEt]LRF (A), were tested for their effects on pregnancy. Daily doses of A prevented implantation and/or caused resorption of implanted blastocysts in mated female rats. This effect was dose related and was most evident when given in regimens including days 5–7 or days 9–10 of pregnancy. LRF also has antigonadal effects, but at much higher doses than A. The use of corn oil vs. 0.1% gelatin-saline improved the effectiveness of low doses of A. Termination of pregnancy in A or LRF-treated rats is most probably due to the markedly diminished progesterone secretion, which could result from the secretion of biologically inactive gonadotropins, reduced pituitary responsiveness to endogenous LRF, or downregulation of gonadal receptors for LH.